That's the conclusion of a recent study that examined a group of female college students. The students performed a series of cognitive tests that progressively increased in difficulty. Those who were deficient in iron struggled to keep up.

That makes sense; iron ensures the brain has enough oxygen and energy to perform complex tasks. Yet more than one in ten U.S. women lacks the iron they need. By contrast, just one in 50 men does.

This isn't the only area of nutrition where women lag behind their male counterparts. Nearly four in ten women fail to provide their bodies with all the vitamins and nutrients they need.

A daily multivitamin can help women fill those gaps. Many women can simply add these supplements to their grocery lists. But millions of poor women struggle to do so. Fortunately, policymakers can easily expand access to needed vitamins.

Nutritional deficiencies can cause severe health problems.

Iron deficiency can cause weakness, fatigue, headaches, and shortness of breath - and impede thinking. It can also increase the risk of developing pancreatic, liver, and kidney cancer.

Vitamin D helps prevent osteoporosis, a condition in which the bones become weak and break easily. This condition disproportionately effects women.

In fact, half of all women will experience a fracture from a fall at standing height or less in their lifetime. Vitamin D deficiency is largely responsible; nearly four in ten women are short on this nutrient.

Nutritional deficiencies can particularly harm pregnant or breast-feeding women and their babies, as more nutrients are needed to support healthy fetal and post-natal growth. Alarmingly, nationwide, half of these women don't get enough vitamins.

For one, vitamin A. During pregnancy, the body saps maternal tissue of this vitamin to support fetal growth. So, pregnant women can suddenly find themselves falling short of a critical nutrient that protects vision and the immune system.

Many women lack this nutrient. This deficiency can also hurt the fetus. One study of pregnant women found that those short on vitamin A were less likely to carry their babies to term.

Folic acid, or vitamin B9, supports the development of a baby's brain and spinal cord. Shortages can result in serious birth defects, including paralysis, and even death. Yet nearly three in four women of reproductive age don't get the government-recommended amount.

Eating better can help people dodge these risks, of course. But millions of poor women struggle to access healthy food. Fast food is easier and cheaper.

For many women, buying cheap food is the only financially feasible option. One in eight women lives in poverty, compared to one in ten men. Women are also more likely to live in extreme poverty.

That's why multivitamins are critical. One review of over 10,000 women concluded that those who took iron supplements were less likely to be anemic than those who did not.

Another review found that calcium plus vitamin D supplementation reduced the risk of all fractures by 15 percent and hip fractures by 30 percent.

For low-income women who would struggle to buy multivitamins, policymakers could easily help by expanding the list of what's covered by the Supplemental Nutrition Assistance Program.

Doing so would come at very little cost to the government. But it would drastically improve health.

Millions of women aren't getting the vitamins they need. Multivitamins offer a solution.